Aerodynamics is a prime consideration in the design of vehicles. There are several factors that contribute to the aerodynamic drag caused by friction of air flowing around the sides of a truck or vehicle. A key to minimizing drag is the reduction or elimination of turbulence.
In conventional semi-tractor vehicles, the transition between the front fenders and the chassis fairing is often fairly abrupt due to the cab access steps. This leads to airflow separation and increased drag. To minimize this effect, the access steps are often reduced in size and/or the steps are placed in shallow recesses in the vehicle body. This makes the steps more difficult to use.
To improve the aerodynamic performance of cab access steps, a number of concealed or deployable step designs have been proposed for semi-tractors. These designs employ mechanical linkages or actuators of various types to expose or extend steps from a compact or flush position upon opening the semi-tractor door to the cab. However, many of these systems are complex in nature due to the mechanisms.
In addition to the aerodynamic drag caused by access steps, the interface between the cab and chassis also contributes to the aerodynamic drag of the vehicle. In conventional semi-tractors, this interface is typically a horizontal gap created between the bottom edge of the cab and the top of the chassis. Air is drawn into the horizontal gap, which then exits the rear of the cab and into the gap between the cab and semi-trailer. The air hitting the front of the semi-trailer causes increased aerodynamic drag.